Production of sodium cyanamideformaldehyde condensation product



Patented Nov. 19, 1946 NT c rries FORMALDEHYDE CONDENSATION PROD- UCT Joseph Frederic Walker, Lewiston, N. Y., assignor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application 'July 4,1945,

\ Serial No. 603,255

scams. 01. 260-42) This invention relates to a new and improved sodium cyanamide-formaldehyde condensation product, and method for producing-same. The product of this invention has particular utility as a brighteningagent in the electroplating of zinc.

In my copending -application Serial No. 507,- 182, filed October 21, 1943, I have disclosed the sodium cyanamide-formaldehyde condensation product produced by reacting sodium cyanamide (NazCN2), as such, with formaldehyde in sub stantially equimolecular proportions in an aqueous reaction medium. Although the product pro duced in accordance with that process is greatly. superior as a brightening agent for certain electroplating solutions than similar condensation products, for example, the product-produced by the process of Schmidt Patent No. 1,791,434, numerous difliculties have been encountered in producing a product of consistently good quality. The process of my prior, above-identified application often resulted in a product which was highly compressible and difflcult to wash and filter. The said product was extremely heat-sensitive when wet and often could not be-satisfactorily dried with an air drier or oven drier without objectionable resinification to a dark, opaque material. a

It is an object of this invention to produce a sodium cyanamide-formaldehyde condensation product which has a satisfactory heat stability, and which will function satisfactorily as a brightening agent in zinc plating from a zinc cyanide plating bath or from an acid type zinc bath.

It is another object of this invention to pro duce a sodium cyanamide-formaldehyde condensation product which can be satisfactorily air dried or oven dried without objectionable resiniflcation.

It is another object of this invention to produce a' sodium cyanamide-formaldehyde condensation product which can be readily washed and filtered, which can be satisfactorily air dried or oven dried, and which will function satisfactorily as a brightening agent in zinc plating from a zinc-plating bath.

It is another object of this invention to provide a process for the production of a sodium cyanamide-formaldehyde condensation product which process can be readily controlled to produce a product of consistently good quality.

Other objects of the invention will appear hereinafter.

The objects of this invention may be accomplished, in general, by reacting, in aqueous solution and at a temperature below 45 0., approximately equimolecular amounts of monosodium cyanamide and formaldehyde, and precipitating the resulting condensation product by the addition of sufiicient strong acid to reduce: the pH of the mixture to between 8 and 9.

As stated in my copending application, the product is probably a partially hydrated polymer of methylene cyanamide (CH:=NCN) in which approximately two-thirds of the CN radicals have been converted to amide groups. Analyses for carbon, hydrogen, and nitrogen indicate that its composition closely approximates the empirical formula, C6Hi0N602. The characteristics of the product are those of an amorphous resin, and it is probably not a simple compound of low molecular weight but rather a polymer or mixture of polymers made up of units corresponding to the CeHmNeOa formula. It is believed that the structural formula of this polymer unit is as follows:

Despite the fact that the product of this application is believed to have approximately the same empirical formula as that of my copending application, there are some chemical or physicaldiflerences between these products as is evidenced by the fact that the product of this invention is considerably more heat stable, and approximately one-half the quantity of the product of this invention will have the same brightening characteristics in a zinc cyanide plating process as a given quantity of the product obtained ,by the process of my above-said copending application.

In accordance with .the preferred process for the production of the product of the present invention, equivalent amounts of NazCN: and a strong acid are reacted in aqueous solution at a temperature between 5 C. and 45 C., to form reaction is complete, the sodium cyanamideformaldehyde reaction product is precipitated by the addition of sufllcient strong acid to lower the pH value of the reaction mixture to between 8 and 9. The resulting slurry is then filtered and the solids washed with water and dried. I

The strong acid used in forming the monosodium cyanamide, or in precipitating the cyanamide-formaldehyde reaction product, is preferably hydrochloric acid. However, sulfuric acid, phosphoric acid or acetic acid may also be used to good effect. Preferably, the acid used is in aqueous solution, for example 15% to 37% HCl or 20% to 60% H2804, and in the said two steps the acid used should preferably be the same acid.

As stated above, the formation of the monosodium cyanamide and the reaction between it and formaldehyde is carried out inaqueous solution. These aqueous. solutions may be, optionally, substantially saturated solutions or relatively weak solutions, the only considerations being that the pH of the solution is at least 9.5, and preferably about 10.5, and the economy and ease of handling and manipulation of the reactants and products.

In order to obtain a reasonable yield and avoid unnecessary decomposition of reactants or reaction products, both the, formation of monosoprecipitation of the reaction product is preferably carried out at a temperature below 30 C.

Example I One gram mole of monosodium cyanamide was added to one gram mole of formaldehyde in the form of a 12% aqueous solution having a temperature of 0 C. to 10 C. After a reaction period of 1.5 hours at a temperature between 10 C. and 30 C., the mixture was chilled to a temperature of 10 C. and 37% hydrochloric acid added, while agitating the mixture, until the mixture had a pH value of between 8 and 9. A white precipitate separated from the solution. After standing over- The formaldehyde added to the aqueous solution of monosodium cyanamide may be in the form of an aqueous solution of formaldehyde of the type commercially marketed or of other concentration. or it may be in the form of para formaldehyde, or other polymer of formaldehyde which will readily form formaldehyde under the conditions of the reaction. Reference to the use of formaldehyde as a reactant throughout the specification and claims is, therefore, meant to include formaldehyde, paraformaldehyde, and other linear polyoxymethylene-type polymers.

After acidification of the products of the reaction to a pH of between 8 and 9, the precipitated reaction product will form a slurry in the liquid medium. Preferably, the precipitation is allowed to proceed for a period of two hours or more to insure complete precipitation. The slurry is then filtered, for example, by means of a suction filter, or equivalent filter, and the filter cake is preferably'reslurriedsix to eight times with tap water and the wash water removed by filtration and/or decantation. The washed filter cake may be dried by placing the same on a screen, for example, a 16-mesh screen and positioning the screen in an air drier in which the air at a temperature of between 40 C. and 75 C. is passed into contact with the filter cake, or through the same, until moisture content is below 5%. The temperature of the air in the drier may be raised somewhat during the last stages of the drying operation.

' The drying may also be carried out in a convennight to insure substantially complete precipitation, the precipitate was filtered off, washed with water and dried in a vacuum desiccator, the yield of product was 45.7 grams, and represents a yield of 0.71 gram product per gram of monosodium cyanamide.

Example II One mole (90.5'grams) technical grade sodium cyanamide was dissolved in 200 cc. water at 0 to 10 C. Eighty-three (83) cc. concentrated hydrochloric acid (one mole HCl) was added dropwise to the cold solution while shaking the same in a flask. Then 81 grams of 37% formaldehyde solution (one mole formaldehyde) was slowly added to the cold solution while stirring and the reaction allowed to proceed for a period of 3.5 hours during which the temperature of the reaction mass was not allowed to exceed 40 C. The solution was then chilled to a temperature of about 10 C. and concentrated hydrochloric acid was added until the pH value of the solution was between'8 and 9. The mass was allowed to stand overnight after which the resulting precipitate was filtered oil. The filter cake was washed with water and dried in a vacuum desiccator.

Weight of product 49.20 grams Yield 0.54 gram/g. NazCNz Example III the addition of formaldehyde was completed (30 2 minutes) the reaction mixturewas treated with 40% aqueous sulfuric acid until the pH was-between 8 and 9. After maintaining the resulting reaction mixture at a temperature of, about 25 C. for one hour to allow precipitation to take place, the solid product was filtered off, washed with water and dried in a vacuum desiccator. A second crop of precipitated solid was removed after another fourteen hours and a third crop two days later.

About 7% of the formaldehyde ed remained in the filtrate.

Results were as follows:

Weight of first crop 28.8 grams Weight of second crop 16.3 grams Weight of third crop 1.0 gram Weight of total 46.1 sitar Yield 0.51 gram/g.NazCNz Example IV 1. The sodium cyanamide-formaldehyde reaction product is produced by the following four steps:

(a) A solution of 286 pounds of sodium cyanamide in 450 pounds of city water is prepared in a jacketed reactor equipped with an anchor-type agitator. Rates of cyanamide feed and flow of coolant in the jacket are regulated to maintain the temperature at 30 C. to 35 C.

(b) Following the addition of NazCNz, the solution is agitated for thirty minutes, cooled to C., and neutralized with 24% H01 to NaHCNz, the rates of acid feed and coolant being regulated to maintain the temperature at 28 C. to 35 C. Following the neutralization, the solution is cooled to 10 C.

(0) One hundred (100) pounds of 96% formaldehyde is added in two equal portions, and the cooling is regulated to limit the temperature to a peak of 33 C. to 35 0., following each addition. The charge is then cooled to C.

(d) The product is precipitated by neutralizing the solution to a pH of 9.0 with 24% B01 while the temperature is maintained at 18 C. to 21 C. The slurry is agitated for one hour, dropped to a Nutsch filter, and a volume of city water, equal to the volume of slurry, is added.

2. The cyanamide formaldehyde reaction product is collected,washed, and dried according to the following procedure:

(a) Vacuum is applied to the Nutsche and the filtrate is removed, partially by decantation as the solids settle, andpartially by direct filtration.

(b) The filter cake is reslurried six to eight times with city water, and the wash water is removed by filtration and decantation.

(c) The washed filter cake is dried on 16-mesh screen in an air drier at 60 0., until the moisture content is less than 10%. Drying is continued at 65 C. to 70 C. until the moisture is below 5.0%.

(d) The dry product is discharged from the drier as small lumps and reduced to minus 40 mesh in a micro-pulverizer.

Although the product of the present invention has many other uses such as the use as a flameproofing agent, use in the manuiacture of heatresistant resins, use as an' acid-inhibitor in the pickling of steel, it has particular utility as a brightening agent in electroplating processes, especially in electroplating processes employing metal cyanide salt plating baths. Tests have been carried out to determine its utility as a brightening agent in zinc electroplating both from zinc cyanide plating solutions and from acid zinc electrolytes. In a zinc cyanide plating process it is highly desirable to combine a sodium cyamide-formaldehyde condensation product with a small amount of low viscosity po yvinyl alcohol and add such mixture to the plating bath as a brightening agent. Usually, 90% to 99% of the condensation product is added to 10% to 1% of polyvinyl alcohol having a saponification number between 0 and 18, and a small amount of this mixture is added to the zinc plating bath. When.

used as a brightening agent in the acid zinc electrolytes no polyvinyl alcohol is added. The brightening agent, in such processes, has particular utility in producing a bright plate at varying current densities. A great variation in current densities cannot be avoided in plating ob jects of irregular outline.

The product of the present invention may be used in considerably smaller quantity in zinc plating baths to produce a given brightness than the sodium cyanamide-formaldehyde condensation product of my above-mentioned copending application.

A comparison of the two products with regard to their efiective concentration in a zinc cyanide plating bath, the percentage content of chloride (as NaCl) in the product, and the percentage of water in the product is given below:

The product of the present invention can be air dried at a given temperature with only occasional occurrence of resinification, and the degree of resinification is negligible. In several experiments the reaction temperature has been allowed to reach 40 C. to 42 C. with no apparent deleterious effect except that the product becomes slightly discolored (pink to orange). Since the reaction, in accordance with the present invention, proceeds at a pH of about 10.5, difllculties with poor heat stability have been largely eliminated. The resulting precipitated product appears to be looser than the similar product produced by previously known processes and. is not a highly compressible and, therefore, is more readily washed and filtered.

Throughout the specification and claims reference to parts, proportions and percentages is meant to refer to parts, proportions and percentages by weight unless otherwise specified.

Since it is obvious that many changes and modifications can be made in the above-described details without departing from the nature and spirit of the invention, it is to be understood that the invention is not to be limited thereto, except as set forth in the appended claims.

I claim:

1. The process for the production of a sodium I cyanamide-formaldehyde condensation productwhich comprises reacting, in aqueous solution and at a temperature below 45 0., approximately equimolecular amounts of monosodium cyanamide and formaldehyde, and precipitating the resulting product by the addition of sumcient strong acid to reduce the pH of the mixture to between 8 and 9.

2. The process for the production of a sodium cyanamide-formaldehyde condensation product' which comprises reacting, in aqueous solution having a pH above 9.5 and at a temperature below 45 (2., approximately equimolecular amounts of monosodium cyanamide and formaldehyde, and precipitating the resulting product by the addition of suillcient strong acid to reduce the pH of the mixture to between 8 and 9.

3. The process for the production of a sodium cyanamide-formaldehyde condensation product which comprises reacting, in aqueous solution below 45 0., approximately equimolecular amounts of monosodium cyanamide and formaldehyde. and precipitating the resulting product by the addition or sufllcient strong acid to reduce the pH of the mixture to between 8 and 9.

4. The process for the production of a sodium cyanamide-formaldehyde condensation product which comprises reacting, in aqueous solution. approximately equivalent mounts of sodium cyanae mide and a strong acid whereby to produce an aqueous solution of monosodium cyanamide havinz a pH above 9.5, reacting the resulting solution, at a temperature below 45 C., with an amount of formaldehyde approximately equimolecular with said sodium cyanamide, and precipi- 8 tating the resulting product by the addition a suilicient strong acid to reduce the pH oi the mix ture to between 8 and '9.

5. The product obtained by tin: process cl 6 claim 1.

10 polyvinyl alcohol having a saponiilcation number between 0 and 18.

8. The product obtained by the process or claim 4 admixed with 1% to 10% by wei ht or polyvinyl alcohol having a saponiflcation number 15 between 0 and 18.

JOSEPH FREDERIC 

